1. Field of the Invention
The invention relates to a method for the use of a packaging apparatus.
The invention also relates to a packaging apparatus for practicing the method.
2. Description of Background Art
Such a method and apparatus are known from U.S. Pat. No. 3,589,091. In particular FIG. 14 and the passage in column 8, lines 27-63 thereof show and describe an apparatus with which products are packaged in a film which is supplied in a continuous web and which is stretched before the film is folded around the articles to be packaged. For the purpose of stretching the film, two pairs of drawing rollers 161, 162 are used, while one pair of drawing rollers located downstream are rotated at a higher speed than the pair of drawing rollers located upstream. What is thus achieved according to the US patent, is that the film is stretched. However, the US patent does not clarify in what manner the film web is supplied and in what manner the degree of stretching is determined. Without an accurate control of the transport of the film web downstream of the pair of drawing rollers and upstream of the pair of drawing rollers, with time, the film web will break or, conversely, sag upstream or downstream of, or between the pairs of drawing rollers.
Another drawback of the known apparatus and method is that the film shrinking back already occurs after the film has passed the downstream pair of drawing rollers 162. In particular when the film is supplied from below and is guided over a film guiding element for bringing the film in a horizontal plane, shrinking causes an irregular run, leading to tracking problems. Also when the apparatus is stopped, the film downstream of the downstream pair of drawing rollers 162 will have ample time to shrink back. What this leads to is that the first packages which are processed after restarting of the apparatus will not be tight-fitting packages, or that they can even be damaged.
The present invention contemplates a practical solution to these problems.
In practice, the packaging apparatuses marketed hitherto by applicant and the method utilized therewith yield packages in which the products are loosely enveloped by the film package. To the present day, with these known apparatuses, only one pair of drawing rollers was used for unrolling the film web from the film web roll. With the packaging apparatuses marketed by applicant, the loosely enveloping packages are the result of the fact that the cross sealing device is provided with sealing bars having a particular width, so that the products present in the package tube must be spaced at a particular distance from each other. Moreover, the cross seal has to be applied while the package tube moves in the transport direction at a speed of approximately 1.5 meters per second. That is why a space of almost 30 mm is required between two successive products plus the thickness of the product. All this results in two flaps at the end faces of the products, having a length of approximately 15 mm. Such flaps cause problems in the sorting machines of the postmen and, what is more, a non-tight-fitting package is less esthetic than a package in which the product is received in a tight-fitting manner.
To solve these problems, often, downstream of the packaging apparatus, a so-called shrink tunnel was utilized. In such a shrink tunnel, the packaged products are exposed to a high temperature under the influence of which the packaging film shrinks. Drawbacks of this known solution are that a shrink tunnel requires a high investment, that the use of the shrink tunnel demands a lot of energy and that, generally, shrink tunnels take up much space in a production facility, which is undesired. Moreover, special shrink film has to be utilized which is relatively expensive.
The apparatus known from the US patent forms a possible solution to the problems of too loose-fitting packages, that is, by stretching the film prior to folding. However, this known solution has the associated drawbacks already described.